Java if else

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The if Statement:

An if statement consists of a Boolean expression followed by one or more statements.

The syntax of an if statement is:

if(boolean_expression) {
   //Statements will execute if the Boolean expression is true
}

If the Boolean expression evaluates to true then the block of code inside the if statement will be executed. If not the first set of code after the end of the if statement (after the closing curly brace) will be executed.

Exampl

class IfStatement {
    public static void main(String[] args){
        int x = 10;
        if(x == 10){
            System.out.println("X is equal to 10");
        }
    }
}

The Output is
X is equal to 10

if else Statement 

An if statement can be followed by an optional else statement, which executes when the Boolean expression is false.

if(boolean_expression){
   //Executes when the Boolean expression is true
}else{
   //Executes when the boolean expression is false
}

Example 

class IfElseStatement {
    public static void main(String[] args){
        int x = 12;
        if(x == 10){
            System.out.println("X is equal to 10");
        }else{
             System.out.println("X is Not equal to 10");
        }
    }
}

Out put is
X is Not equal to 10

The if else if else Statement

An if statement can be followed by an optional else if...else statement, which is very useful to test various conditions using single if...else if statement.

When using if , else if , else statements there are few points to keep in mind.

• An if can have zero or one else's and it must come after any else if's.
• An if can have zero to many else if's and they must come before the else.
• Once an else if succeeds, none of the remaining else if's or else's will be tested.

The syntax of an if else if

if(Boolean_expression 1){
   //Executes when the Boolean expression 1 is true
}else if(Boolean_expression 2){
   //Executes when the Boolean expression 2 is true
}else if(Boolean_expression 3){
   //Executes when the Boolean expression 3 is true
}else {
   //Executes when the none of the above condition is true.
}

Example 

class IfElseIfStatement {
    public static void main(String[] args){
        int x = 12;
        if(x == 10){
            System.out.println("X is equal to 10");
        }else if(x==11){
             System.out.println("X is equal equal to 11");
        }else if(x==12){
             System.out.println("X is equal equal to 12");
        }else{
            System.out.println("X > 12");
        }
    }
}

Output is
X is equal equal to 12

Nested if else Statement

A nested if statement is an if-else statement with another if statement as the if body or the else body.

The syntax of Nested if else

if(Boolean_expression 1){
   //Executes when the Boolean expression 1 is true
   if(Boolean_expression 2){
      //Executes when the Boolean expression 2 is true
   }
}

Example 

class NestedIfElse {
    public static void main(String[] args){
        int firstValue = 12;
        int secondValue = 20;
     
        if(firstValue ==12){
            System.out.println("First Value is 12");
            if(secondValue == 20){
                System.out.println("Second Value is 20");
            }
        }
     
    }
}

Output is
First Value is 12
Second Value is 20

The switch Statement

A switch statement allows a variable to be tested for equality against a list of values. Each value is called a case, and the variable being switched on is checked for each case.

The syntax of switch statement

switch(expression){
    case value :
       //Statements
       break; //optional
    case value :
       //Statements
       break; //optional
    //You can have any number of case statements.
    default : //Optional
       //Statements
}

The following rules apply to a switch statement

The variable used in a switch statement can only be a byte, short, int, or char.

• You can have any number of case statements within a switch. Each case is followed by the value to be compared to and a colon.
• The value for a case must be the same data type as the variable in the switch and it must be a constant or a literal.
• When the variable being switched on is equal to a case, the statements following that case will execute until a break statement is reached.
• When a break statement is reached, the switch terminates, and the flow of control jumps to the next line following the switch statement.
• Not every case needs to contain a break. If no break appears, the flow of control will fall through to subsequent cases until a break is reached.
• A switch statement can have an optional default case, which must appear at the end of the switch. The default case can be used for performing a task when none of the cases is true. No break is needed in the default case.

class SwitchStatement {

    public static void main(String args[]) {
        int value = 10;

        switch (value) {
            case 5:  System.out.println("Value is Five");
               break;
             
            case 10: System.out.println("Value is Ten");
                break;
            case 15: System.out.println("Value is fivtean");
                break;

        }
        System.out.println("Your value is > 15");
    }
}

The Output is :-
Value is Ten
Your value is 10